Short throw projection lens with a dome

Abstract

The present invention relates to an outer dome configured to provide protection and optical correction to a system of projection optics and the output thereof. More particularly, an optical projection system having an optical offset of greater than 100% is comprised within a projector housing having an outer dome comprised of an optically active material mounted onto an opening approximately coinciding with the optical projection system's exit pupil. The outer dome is configured to be decenterized from the exit pupil (e.g., the center of the dome is offset from the exit pupil in one or more of an x, y, and z direction) such that it provides optical correction to a projected image. Therefore, an outer dome is configured to provide protection to optical elements provided therein and improvement of projected image quality (e.g., reduced image distortion, reduced aberration).

What is claimed is: 
     
       1. A method of projecting an image onto a display surface with an image offset of greater than 100% and a throw ratio of 0.15 or less, comprising:
 providing an illumination source, a spatial light modulator and projection optics within a housing having an opening; 
 modulating light received from the illumination source using a spatial light modulator; 
 projecting the modulated light with the projection optics along an optical axis to an exit pupil generally aligned with the housing opening, the projection optics having optical properties to correct for image pixel grid distortion in an image formed by the projected light; 
 providing a light transparent dome mounted over the housing opening providing physical protection for the projection optics and having a center of curvature decentered by an offset in one or more of x, y and z directions from alignment with the exit pupil extending through the optical axis; and 
 transmitting the light projected by the projection optics through the light transmitting dome, the dome having optical properties to further correct for image pixel grid distortion in the image formed by the projected light. 
 
     
     
       2. The method of  claim 1 , wherein the dome has a substantially equal thickness along a solid angle at a portion of the dome through which the projected light passes. 
     
     
       3. The method of  claim 1 , wherein the dome has a spherical curvature. 
     
     
       4. The method of  claim 1 , wherein the dome has a conic curvature. 
     
     
       5. The method of  claim 1 , wherein the dome forms a hermetic seal with the housing. 
     
     
       6. The method of  claim 1 , wherein the projection optics comprises:
 a plurality of aspheric surfaces configured to receive the modulated light and provide a reduction in optical aberration; and 
 a mirror with an aspheric prescription. 
 
     
     
       7. The method of  claim 6 , wherein the plurality of aspheric surfaces are decenterized with respect to the opening. 
     
     
       8. The method of  claim 1 , wherein the projection optics comprises:
 a first lens having an aspheric prescription, wherein the first lens is configured to receive the modulated light from the spatial light modulator and provide some of the partial image edge curvature distortion correction; 
 a second lens having an aspheric prescription, wherein the second lens is configured to receive the modulated light from the first lens and provide some more of the partial image edge curvature distortion correction; and 
 a mirror having an aspheric prescription and a convex surface, wherein the mirror is configured to receive the modulated light from the second lens, spread out the received light, and project the spread out light to form the image onto a display screen. 
 
     
     
       9. The method of  claim 8 , further comprising:
 a fold mirror configured to receive the modulated light from the first lens and to convey the received modulated light to the second lens, thereby reducing the distance from the illumination source to the aspheric mirror. 
 
     
     
       10. The method of  claim 9 , wherein the method is a method for projecting an image in an interactive electronic white board configuration. 
     
     
       11. The method of  claim 9 , wherein the method is a method for projecting an image in a rear projection television. 
     
     
       12. The method of  claim 1 , wherein the modulated light projected by the projection optics passes through a portion of the dome that has a substantially equal thickness. 
     
     
       13. The method of  claim 1 , wherein the illumination source comprises a light emitting diode (LED) die. 
     
     
       14. The method of  claim 13 , wherein the projection optics comprises a plurality of aspheric surfaces configured to provide the partial image edge curvature distortion correction. 
     
     
       15. The method of  claim 1 , wherein the spatial light modulator in off-axis relative to the optical axis. 
     
     
       16. The method of  claim 15 , wherein the spatial light modulator is a digital micro-mirror device. 
     
     
       17. The method of  claim 16 , wherein the projection optics is configured to provide a first order distortion correction to the projected image; and the dome is configured to provide a second order distortion correction to the projected image.